Heavy duty snap-acting thermostat



Feb. 6, 1940. K, CLARK 2,189,627

HEAVY DUTY SNAP-ACTING THERMOSTAT Fil ed March 25, 1938 4 Sheets-Sheet 1I I TOR 21? i EarZ XQJYa IK.

Feb. 6, 1940. E. K. CLARK HEAVY DUTYSNAF-ACTING THERMOSTAT Filed March25, 1938 4 Sheets-Sheet 2 WITNESSES: 6 4 M.

H ATD'TORNEY Feb. 6, 1940. E. K. CLARK 2,189,627

HEAVY DUTY SNAP-ACTING THERMOSTAT Filed March 25, 1938 4 Sheets-Sheet I5[nsulatiwz I 7 7 /2 3 J74 2x 1 WITNESSES: fem/20 .4 77 INVENTOR 9? EarlK 670/24.

' Patented Feb. 6, 1940 UNITED STATES PATENT OFFICE HEAVY DUTYSNAP-ACTING THERMOSTAT vania Application March 25,

11 Claims.

My invention relates to snap-acting thermostats, and more particularlyto a heavy-duty snap-acting thermostat; particularly adapted for use inwater heaters.

An object of my invention is to provide a sensitive snap-actingthermostat which may be mounted directly against a water tank wall andoperate with a bimetal to water temperature ratio of 1:1, in contrastwith the now well- 10 known method of mounting such thermostats on thehead of the water heating element, which, therefor have a bimetal towater temperature ratio of, say 2:1.

A further object of my invention 'is to provide 15 a heavy-dutysnap-acting thermostat which will have a uniform average temperaturerange of operation with a constant amplitude over its whole range, sothat such thermostat may be marked directly in degrees, such asFahrenheit go or centigrade.

A further object of my invention is to provide a positive-actionsnap-acting heavy-duty thermostat capable of handling at least five kw.of power with a low heating rate of say, from about '5 to .15 degreesper hourand a cooling rate of,-

say, 2 degrees per hour.

A further object of my invention is to provide a snap-acting thermostathaving a plurality of springs or resilient members compressed 30 intoelastic curves between rigid supports for producing the snap action ofsuch thermostat by eliminating frictional factors and by Possessing afreedom of overcenter action.

A still further object of my invention is to 35 provide a snap-actingthermostat .having a plurality of springs or resilient memberscompressed into elastic curves between rigid supports, whereby suchmembers cannot be jarred loose from such supports soas to alter thecalibration 40 of the thermostat; thus producing a thermostat which willhave a permanent calibration.

A further object of my invention is to provide an elastic or resilientsupporting member for exerting a decreasingly biasing action upon adevice supported thereby as the device andresilient member move awayfrom a given position.

This action, in turn produces a snap action of the supported devicewithout any frictional en- E sement between such device and resilientmember.

A further object of my invention is to provide a resilient member whichwhen rigidly attached to a movable device vwill prohibit the movement 55of such device in the plane thereof but will per- 1938, Serial No.198,077

mit and ensure snap-action of the device in a direction normal to theplane thereof.

A further object of my invention is to provide a thermostat in which thecontact pressure does not diminish to zero at the snapping temperaturebut maintains a minimum irreducible contact pressure until switchingtakes place by impact.

Other objects of my invention will either be pointed out specifically inthe course of the following description of a device embodying myinvention, or will be apparent from such de scription.

In the accompanying drawings:

Figure 1 is a top plan view of a device embodying my invention;

Fig. 2 is a side view, partially in elevation and partially in section,taken along the broken line II--II of the device shown in Fig. 1;

Fig. 3 is a sectional view taken along the line III-III of Fig. 2;

Fig. 4 is a view similar to Fig. 3 with the device in' one of itsoperative positions;

Fig. 5 is a fragmentary view, taken along the right-hand end of the lineII-II of Fig. 1, with the device in its second operating position;

Fig. 6 is a sectional view taken along the line VI-VI of Fig. 2;

Figs. 7, 8 and 9 are enlarged elevational views of portions of thedevice shown in Figs. 1 and 2;

Fig. 10 is a sectional view taken along the line XX of Fig. 9;

Fig. 11 is a sectional view taken along the line X[X[ of Fig. 10;

Figs. 12, 13 and 14 are elevational views of various parts incorporatedin the device shown in Figs. 1 and 2;

Figs. 15 and 16 are top plan views of two members constituting parts ofthe device embodying my invention;

Figs. 17 and 18 are views indicating various positions of portions ofthe device embodying my invention;

Fig. 19 is an elevational and partial sectional View illustrating themounting of a bimetallic member in the device shown in Figs. 1 and 2;

Fig. 20 is an enlarged partial elevational view taken in the directionindicated by line XX-IQI of Fig. 19; and

Fig. 21 is a graph illustrating the operating principle of the deviceembodying my invention.

Referring to the accompanying drawings, I show a heavy-duty water heaterthermostat or instantaneous thermo-switch I0 including 9. casing l2, aninner insulating switch support mem- 55 ber I4 having mounted thereonstationary coned near one end on resilient member 22 and operativelyassociated with an impact pin assembly 25. The impact pin assembly 25includes an impact pin 24 which is rigidly attached to a secondresilient member 26 and operatively associated with a heat-responsivedevice 28.

As is hereinafter described in greater detail, and as shown in Figs. 1to 6, inclusive, and 21, the movable contact arm is rotatably attachedat one end to the inner insulating switch support member I4 andoperatively associated with the impact pin assembly 25 at the other end.A resilient member 22 is rigidly attached to the movable contact arm 20and to an adjusting screw assembly 52 which in combination act as asecond support for the contact arm 20. A movable contact H, mountedintermediate the ends of arm 20, selectively engages either pair ofstationary contacts IE or l8 as the contact arm 20 moves in response tothe movement of the operatively associated impact pin assembly 25. Theresilient member 22 through the cooperative action of adlusting screwassembly 52 biases the contact arm 20 so that the movable contact I!will always have a positive contact pressure with either cooperatingstationary contact IE or l8, and produces a snap-action of the contactarm 20 as it is moved from one operating position to another. Inaddition, the impact pin assembly 25, including the frictionlesslyoperating resilient member 28, is operatively associated with the heatresponsive device 28 and transmits the movements of such device to thecontact arm 20. The resilient member 26 applies a force to the impactpin assembly 25 and heat responsive device 28 which tends to hold themin one of their limiting positions, and as they move, to decreasinglyresist the movement thereof away from said position. This in turnproduces a snap action of the impact pin assemture 32 bly 25 and heatresponsive device 28 as the temperature of the device reaches apredetermined operating value. Inasmuch as the contact arm 20 isoperatively associated with the impact pin assembly 25, and, therefore,the heat responsive device 28, the contact arm 20 will be moved from oneoperating position to another in response to the movements of heatresponsive device 28. This movement will be snap acting in bothdirections,

due to the combined action of resilient member 22..

and the snap action of the impact pin, assembly 25.

Referring to the thermostat Ill in greater detail, the casing I2 ispreferably made of a diecast construction and of such metallic materialthat it will withstand severe mechanical shock cated by the referencecharacters I41: and I412.

Member l4 supports the movable contact arm 20 and stationary contacts l6and I8, as hereinafter described'in detail. Member I4 is rigidlyattached to the casing l2 by a plurality of screws IS. The inner supportmember l4 has an aperextending vertically therethrough,

- stantially directly below the two contacts 18 and spaced apredetermined distance apart therefrom. The movable contact arm 20,having contacts H insulatedly attached thereto, is mounted upon thesupporting member 84 in such a manner that contacts I! will be free toengage either set of the stationary contacts 16 or H], as hereinaftermore fully described.

The movable contact arm 20, shown in detail in Fig. 15, is guided ormovably supported at one endthereof by means of shoulder pin 36, whichfunctions, in this instance, as a fulcrum. The shoulder pin 36, shown inFig. 14, is rigidly attached to the inner support member I4substantially as shown in Figs. 1 and 2. The movable contact arm 20 hasa notch 88, in this instance substantially rectangular in shape,positioned within one end thereof. The notch 88, when operativelyassociated with an annular notch 40, positioned within the shoulder pin36, permits the contact arm' 20 to be supported thereby. 1

The notch 38 located within the movable contact arm 20 is slightlylarger than the notched portion of the shoulder pin 86 but yet smallerthan the main portion of the shoulder pin so that as the arm 20 ispositioned within the notch 40 of shoulder pin 36, the contact arm 20will befree to move or rotate about the shoulder pin as a fulcrum.

The contact arm 20 has a substantially rectangular aperture 42 locatedtherein. The aper-v ture 42 is positioned on the central or longitudinalaxis somewhat near the movable end of the contact arm 20, substantiallyas shown in Fig. 15.

The rectangular aperture 42 is substantially wider than the resilientmember 22 whereby the resilient member 22 may be positioned within orinserted through the aperture 42. A plurality of small circularapertures 44 are located within the contactarm 20 on a transverse axisbisecting the rectangular aperture 42, for attaching the resilientmember 22 to the contact arm 20, as hereinafter described.

The resilient member 22, preferably a flat strip of spring material asshown in Fig. 16, has a plurality of small apertures 44a located nearthe ends thereof. I These apertures 44a permit the resilient member 22,which is longer than the distance between apertures 44 and preferablylonger than the width of the contact arm 20, to be rigidly attached tothe movable contact arm 20 by means of rivets-which extend through theapertures 44a and 44; substantially as shown in Figs. 3, 4 and 6.

Inasmuch as the resilient member 22 is longer than the distance betweenthe apertures 44, lo-' cated within the movable contact arm 20, it isapparent that the resilient member 22, as it is rigidly attached to thecontact arm 28 with the central portion extending through aperture 42,will be biased into and confined to an elastic curve with one endattached to the top surface and the, --:other' end attached to the lowersurface of the contact arm 20, substantially as shown in Figs. 3, 4 and6.

The resilient member 22, when rigidly attached at its ends to thecontact arm 20, will have an unstable position along substantially ahorizontal plane in the center of its configuration. Due to thisunstability, the central portion of the member 22 will tend to move toone or the other of its extreme vertical positions within theaperture42. However, the side walls of the aperture 42 limit this unstablemovement, substantially as shown by dotted lines in Fig. 1'7.

An irregularly shaped aperture 48 is located substantially in thecentral portion of the resilient member 22, as shown in Fig. 16. Aplurality of protruding tongues 50 extend within the aperture 48, for apurpose hereinafter described.

An adjusting screw assembly 52 including screw 53, has a threadedengagement with the insulating inner support member l4 and is preventedfrom turning therein by means of a lock nut 54, substantially as shownin Figs. 2, 5 and 6. The adjusting screw assembly 52 has an annularnotch 56 formed in the lower portion thereof, as shown in Figs. 6, 7, 8and 13. The notch 56 is formed by means of a washer 58 positioned uponthe end of screw 53 whereupon the end is riveted over upon the washer58, as shown at 60 in Fig. 13, rigidly attaching the washer to the Vcontact arm 20 in this neutral position.

screw 53. With the adjusting screw assembly 52 formed in such a manner,it is apparent that such assembly may be inserted within the aperture 48of resilient member 22 before the washer 58 is positioned or rigidlyattached to the lower end of the screw 53.

The tongues 59, located within aperture 48 in resilient member 22,extend within notch 56, as shown in Fig. 8, and permit free rotationalmotion of the adjusting screw assembly 52 relative to the resilientmember 22 after the screw 53 is assembled therewith, but will preventthe rela- The projected Width of the tongues 50 upon I the axis of theadjusting screw assembly 52 is substantially the same as the width ofslot 55, as shown in Fig. 8. However, it is to be understood that thesedimensions are to be such that there shall be no binding actiontherebetween. This prevents relative movement of the resilient member 22along the axis of adjusting screw 53.

The main sides 62 01 the aperture 48, located within the resilientmember 22, when such member is rigidly attached to the movable contactarm 20 and compressed into its predetermined elastic curve, will contactthe outer peripheral portion of the lower end of adjusting screwassembly 52, as shown in Fig. '7, prohibiting any transverse movement ofthe contact arm 20 along its transverse axis with respect to theadjusting screw 53.

Because of the configuration of resilient member 22 when it isoperatively associated with adjusting screw assembly 52, one main side82 will contact the screw 53 above the notch 56, as shown in Fig. '7,while the other main side 52 will contact the washer 58 below the notch56, the washer 58 being equivalent to an extension of screw 53.

It is, therefore, obvious that with the movable contact arm 20 mountedupon insulating support M by means of adjusting screw assembly 52 andresilient member '22, at one end, and by shoulder pin 36 at the otherend, as hereinabove described, such contact arm 20 fwill be prohibitedfrom moving in its plane by reason of the cooperative action of therigidly attached resilient member 22 and adjusting screw assembly 52,and shoulder pin 36. However, it is to be understood that, due to thecontact arm 20 being supported at one end by resilient member 22 and dueto the resiliency of member 22, and its fundamental elastic curvature,the movable end of contact arm 20 will be permitted .to movesubstantially vertically or axially to the adjusting screw assembly 52with a snap action.

The adjusting screw 53 permits the central portion of the resilientmember 22 to be positioned substantially midway between the stationarycontacts i6 and I8. With the contact arm 20 positioned substantially atthe midpoint between the stationary contacts l5 and 18, the verticalbiasing action of the resilient member 22 upon such member 20 will besubstantially zero. In other words, since the vertical biasing action ofresilient member 22 upon contact arm 20 will be substantially zero, thecontact arm 20 theoretically could remain in a neutral position.However, it is to be understood that because of the inherentcharacteristics of member- 22, it would be practically impossible toposition the Accordingly, it will be apparent that this description ofcontact arm 20 is merely for the purpose of explaining the operation ofsuch arm.

Should the contact arm 20, when positioned at a neutral position, beforced either upwardly or downwardly from this neutral position, by someexternal force, the resilient member 22 would become unbalanced. Themember 22 would then force the arm 20 to move in the vertical directionof the externally applied force with an accelerating motion, until themovable contacts I! positioned on arm 25 would engage the stationarycontacts I6 or [8. It is, therefore, obvious that this acceleratingaction of the resilient member 22 upon arm 20 produces a snapactionthereby, and ensures a positive contact pressure at all times.

With the adjusting screw 53, resilient member 22 and contact arm 20adjusted in such a manner, the contact arm 2|] will, when in eitherstatic or limiting position, have an equal biasing action or contactpressure between movable contacts I1 and the cooperating stationarycontact i6 or U.

The amount of this biasing action or contact pressure is shown as C or Cin Fig. 21, and is that force which is exerted by resilient member 22independently of'any exterior or additional forces.

The unstable positions of spring 22, with respect to contact arm 20,within the aperture 42 oi arm 20, produce an equivalent condition ofunstability in contact plate 20 with respect to its movement betweenstationary contacts I6 and I8, when resilient member 22 is supported byadjusting screw 53, as hereinabove described. It, therefore, followsthat after screw 53 has been properly adjusted, moving contact assemblyII has a position of instability at the center of its travel, midwaybetween contacts [8 and I8, and that contact I! is biased equally intoengagement with both the upper pair of stationary contacts i6. and thelower pair of stationary contacts 13.

The correct adjustment of screw assembly 52 is obtained by the verticalmovement of the screw 53 in threaded engagement with insulating switchsupport i4 and is such that the component of force of resilient member22 in the direction of the adjusting screw axis will be zero when theThe guide member all shown in Figs. 10 and 11v has a plurality ofupwardly or vertically extending guides 6| located thereon and avertically extending aperture 63 therethrough. A verticallyextendinginsert I6 is positioned within the aperture 83, and has avertically extending threaded aperture 66 positioned substantially inthe center thereof. The guide member, including insert II, is thenthreaded on the upper threaded por-- tion III of impact pin 24 by meansof the threaded aperture 86 in insert 19.

Inasmuch as the guide member 60 has a threaded engagement with impactpin 24, such guide member may readily be adjusted to any desiredposition thereon. This structure permits the central portion of theresilient member 26, operatively associated with the guide member 60 ashereinafter described, to be movably adjusted with respect to its endsupports 18. This structure, in turn, permits the resilient member to bepositioned at such a point with respect to pin 24 that such pin willmove an equal distance above and below a neutral plane.

The second resilient member 26 is preferably a flat strip of springmaterial and is rigidly attached at its ends to the casing ID by meansof rivets 16, or the like, and likewise rigidly attached atsubstantially the center, to the impact pin assembly 25, as hereinafterdescribed and as is clearly shown in Fig. 3. This resilient member 26 isforced to retain the double symmetrical elastic curve, as shown in Fig.3, due to the cooperative action of the impact pin assembly 25 and therigid end supports, as hereinafter described. The impact pin assemblyforces the resilient member to substantially retain this elasticcurvature which would otherwise assume a stable form of curvature.

The resilient member 26 is longer than the distance between its rigidsupports on rivets 16. It, therefore, follows that the member 26 if notrestrained, would then, when forced longitudinally inwardly from eitherone or both ends, as

sume one ofmthe limiting stable elastic curves shown by dotted lines 21'and 21', in Fig. 18, or a curve similar to 22 shown in Fig. 6. It isunderstood that such member may assume a position which would be thereverse of the curve, as shown by 22 in Fig. 6.

It is, therefore, obvious that, should the central portion of theresilient member 26 be retained substantially in a plane parallel to themember ,26 or in a curvature other than that which such member wouldnormally assume, such member will be restrained or prohibited fromassuming one of its normal stable elastic curves as the endsthereof arebiased inwardly. However, it is to be understood that, due to theinherent characteristics of the resilient member" 26,'such member willattempt to assume one of the stable elastic curves 2'! or 21', dependingon which side of the neutral the central portion is positioned inrespect thereto.

It, therefore, follows that, as the central portion of the resilientmember attempts to assume a curve similar to 21 or 21', it will exert aforce normal to the plane of such resilient member. The force so exertedby the resilient member 26 willbe substantially directly proportional tothe distance of travel of the central portion of such member from itsneutral position. 'This is clearly shown by Fig. 21. In other words, itis to be understood that the closer the central portion of the.resilient member be biased to a central or neutral position, from thenormal assumable curvature, the less such vertical force will be. Theresilient member 26 compressed intothe stable elastic curve produces afreedom of overcenter action.

It, therefore, follows that the vertical biasing force of the resilientmember 26 may also be varied by adjusting the horizontal force. Thisforce value may be adjusted in an additional manner; namely, byadjusting or varying the positions of the end supports, it beingunderstood that the closer such supports are positioned (or moved)towards the central portion, or in this instance towards the impact pinassembly. 25, the greater the horizontal force. Accordingly. ashereinabove described, the vertical force will be increased. Thevertical force may also be obviously reduced, by moving the end supportsof resilient member 26 away from its central portion.

It is obvious that the greater the vertical or normal displacement ofthe central portion of the resilient member, the greater will be theforce required to move such central portion toward its neutral, and thatthe closer such central portion approaches the neutral, acorrespondingly smaller amount of force will be required to continue themovement. In other words, as hereinabove described, the vertical biasingforce of the resilient member 26 is substantially directly proportionalto the vertical displacement of the center of such spring from itsneutral or dead center position. Accordingly, should the central portionbe biased towards the neutral with a sub stantially constant value offorce, it follows that the resilient member 26 will be accelerated dueto the net acting or accelerating force. This condition results in anenergy of motion, which,

in addition to the applied substantially constant force, will cause thecentral portion to pass through the neutral. The inherent action of theresilient member 26 will then aid the applied force, resulting in thecentral portion travelling with a continued acceleration.

It is to be understood that the so-called neutral position of thecentral portion of the resilient member 26 will be that position fromwhich both the relative upward and downward biasing forces of theresilient member will be equal, or that position in which the centralportion would be in when it exerts a zero vertical force component. Inthis instance, this neutral position is substantially in a straight linewith the end supports or rivets 16. The resilient member 26 is confinedto substantially the curvature, shown in Fig. 18, by means of thecooperating action of the impact pin assembly 26 and bimetallic member26. The impact pin assembly 25 has the effect of substantially breakingthe member 26 into two separate resilient members. In other words, theresilient member 26 may be formed of at least two resilient membersmounted in a straight line upona rigid support at one end and upon, say,the impact pin 26 at the other end, it being understood that the twomembers be in a straight line.

This structure then operates as a single mem- Inasmuch as the resilientmember 26 is unstable in this particular curvature, the impact pin 24rigidly attached thereto likewise is correspondingly unstable. Thisinstability results in a tend,-

ency for the resilient member 26, as such member moves from an upper toa lower position, to revert to the form of curvature illustrated by 22.This action results in a corresponding biasing force to be present inthe lower end of impact pin assembly 25. The impact pin assembly 25 thenhas the tendency to wabble or move in a plane normal to and along thelongitudinal axis of resilient member 26. However, inasmuch as the lowerend of impact pin assembly 25 is firmly attached to and restrained frommovement in this plane by the bimetallic member 28, such impact pinassembly 25 will be limited to substantially a vertical movement alongthe axis of impact pin 24.

The resilient member 26 has an aperture located substantially in thecentral portion thereof, not shown. The impact pin assembly 25 isinserted through the aperture in resilient member 26 and rigidlyattached thereto as follows: The upper end of the threaded portion andthe upper end of insert 18, which extends above the guide 80, areinserted through the aperture located within the resilient member 26.The protruding portions 8| and insert 19 in combination with the topsurface of support 80 function, among other things, as a saddle orsupport for the resilient member 26.

A plurality of differential convex washers 82 are positioned above theguide 80 within the up- .wardly extending protruding portions 8| and arein juxtaposition with the resilient member 26, one above such member andone below. A nut 84 positioned on impact pin 24 biases such washersagainst the saddle of guide 80 supporting resilient member 26 in itsdouble elastic curve, substantially as hereinabove described. The nut 84has a recess 81 located in its lower face to permit telescope engagementwith the upper end of insert 18 to ensure adjustable contact with convexwashers 82 at all times. Inasmuch as the nut 84 is threaded on impactpin 24, the position of such nut with respect to guide 88 may be readilychanged, and, according, the shape of the central portion of theresilient member 26 may be readily changed. The changes in shape of thecentral portion adjust the horizontal force exerted by the rigid endsupports of such member. It, therefore, follows that, inasmuch as thevertical force is proportional to the horizontal force exerted by therigid supports, the vertical force transmitted from the resilient member26 to impact pin 24 may be readily adjusted to any desirable value bymerelyv adjusting the position of nut 84.

A look nut 86 may be positioned upon the threaded portion 18 of impactpin 24 to lock the nut 84 imposition, insuring the maintenance of apredescribed elastic position of the resilient member 26 and convexwashers 82, as hereinabove described.

The -heat-responsiv e device 28 is, in this instance, a bimetallicmember, and preferably formed of a flat bimetallic finger or strip,substantially as shown in Fig. 19. The bimetallic member 28 has acircular notch 98 located in one end thereof to cooperate with thetapered notch 14 of the impact pin 24, as hereinafter described. Theother end of the bimetallic member 28 is -member 28 through adjustingscrew 34, at all points throughout its temperature range.

The adjusting screw 34 is rotatably attached to the casing l2 andextends through the insulating support member l4. The screw 34 has athreaded engagement with the bushing 35 which is rigidly attached to thecasing l2. The adjusting screw 34 may then be moved vertically withrespect to the casing l2, as it is rotated within the bushing l2.

If it is desired, a removable scale plate 31 may be positioned upon thesupport member l4. A scale 33 marked in degrees is located upon theplate 31, and is positioned about the adjustable screw 34. A pointer 3|is rigidly attached to screw 34 so that it cooperates with the scale 33,and thus gives a visuable indication of the particular temperaturesetting of the thermostat.

A fulcrum plate 28, shown in Fig. 2, is flexibly attached to the bottomof the adjusting screw 34. The fulcrum plate 29 contacts the bimetallicmember 28, and, as the adjusting screw 34 is raised or lowered withrespect to the casing l2, changes the curvature of the bimetallicmemher. The operating temperatures of the bimetallic member 28 aretherefore changed. The fulcrum plate 29, therefore, operates as an ad-J'ustable fulcrum about which the bimetallic member 28 flexes.Accordingly, the vertical movement of the fulcrum plate 29 resultingfrom the operation of adjusting screw 34 controls the thermal operationof the thermostat l8.

Bimetallic member 28 is initially formed at normal room temperatures toa degree of curvature which will be just annulled at the midpoint of itstemperature range so it will permit the most favorable, substantially 90angular, relationship with the impact pin 24. However, it is to beunderstood that the bimetallic heat-responsive device 28 may be attachedto the casing l2 in any manner desired, so that its movements will bereadily transmitted to the impact pin 24 in a manner as hereinafterdescribed.

The bimetallic member 28 is operatively associated with impact pin 24through the cooperation of circular notch 98 with the tapered annularnotch 14 of pin 24. This cooperation is maintained through the action ofa clip spring which biases the impact pin into engagement with thebimetallic member. The clip spring 16 is preferably of a material havingsubstantially the same diameter as the width of the base of notch 14, asshown in Fig. 20. The clip spring is positioned within the notch 14ofimpact pin 24, and has its ends hooked into notches 13 located withinthe bimetallic member 28, as shown in Fig. 19. This cooperating actionprevents undue longitudinal movement of impact pin 24 with respect tobimetallic member 28.

Relatively unlimited angular movement of bimetallic member 28 withrespect to impact pin 24 is permitted by the tapering of the bimetallicelement 28 beyond the base of annular notch 80, as shown by Fig. 20.This movement is substantially about an axis transverse to thebimetallic member 28 and normal to the axis of the impact pin 24 at: thebase of annular notch 26 flexes about fulcrum plate 29, it will transmita vertical force to the impact pin 24 without any binding action oradditional contact between member 28 and the tapered sides of notch 14.This action provides a free angular movement between the member 28 andthe impact pin 28 without any lost motion relative'thereto longitudinalto the pin.

The bimetallic member 28 is, accordingly, free to flex about theadjusting screw 84 and, therefore, to move the impact pin 24substantially normal to the plane of the bimetal, without undue frictionor binding action between the moving end of the bimetallic member 28 andthe impact pin 24.

As herelnabove described, the compressing of the convex differentialwashers 82 against the guide member 88 controls the lateral compressionof the resilient member 26 against its supports in the casing l2. It,therefore, follows that, inasmuch as resilient member 26 and bimetallicmember 28 are operatively associated, the adjustment of nut 84 directlycontrols the differential of temperature in the bimetallicheat-responsive member 28. This results from the fact that the verticalbiasing action or component of the resilient member 28 is directlyproportional to both its lateral compression and the verticaldisplacement of the center of such resilient member 26 from its neutralor dead-center giositizon, as hereinabove described and shown in Asfurther herelnabove described. the vertical biasing force of theresilient member 26 is directly proportional to the verticaldisplacement of the center of such spring or the vertical displacementof the impact pin 24 from its deadcenter position. In other words,assume in this instance, that, with the impact pin 24 being displacedvertically .03'75 inch from its dead-center position, the verticalbiasing force of the re.-

Fig. 21 shows the conditions whichexist, at a" given operatingtemperature, and those which exist throughout the travel of thebimetallic member 28 and associated parts as they snap from one positionto another atthat same temperature. The bimetallic elastic curve, showntransposed as the dotted line, is above the curve representing theovercenter resilient member 26,

and shows the bimetal and'biasing spring component exactly balanced justprior to its snapping temperature. Fig. 21'represents these conditionsregardless of the direction of operation of the thermostat. It isunderstood that the left side of the graph represents the startingaction of the thermostat.

When the force produced bythe bimetallic heat-responsive device 28becomes slightly greater than the force exerted by spring 26, or in thisinstance,two ounces, it is apparent that such force will overcome thebiasing action of the resilient member 26. The free end of bimetallicmember 28, and the impact pin 24, will then move in a vertical directionor in a direction normal to resilient member 26 until they reach asecond static position. As the impact pin 24 starts moving, the verticaldistance between the original fixed or static position of the resilientmember 26 and the neutral position will be reduced, whereupon thebiasing action of the resilient member 26 toward the original positionwill likewise be reduced, as can be readily seen from Fig. 21. Thisvalue will be zero at the dead center position. The bimetallic force islikewise reduced. However, this force is reduced at a,

lesser rate thanthat of the resilient member 28.

The bimetallic member 28 will, therefore, have a differential orpositive accelerating force, which is represented as D on Fig. 21, whenthe impact pin and bimetal are at their neutral position. Thisaccelerating force produced by the bimetallic member 28, in addition tothe kinetic force. causes the impact pin and member 28 to progressbeyond the neutral position. As they pass the neutral position, theresilient member 26 reverses its action of its forces and aids thetravel. The accelerating force is the net difference between the biasingforce of resilient member 26 and the operating bimetallic member 28, andis directly proportional to the distance moved from the original staticposition at a constant temperature. This condition, in turn, ensures thedesired snap action of the bimetallic member 28 and impact pin 24.

As the bimetallic member 28 changes in, temperature so as to return toits original position, it builds up an equal and opposite force fromthat which it possessed when snapping from its first static position.However, as hereinabove de scribed, the resilient member 26 will,through the cooperation of impact pin 24, hold the bimetallic member inthe second static or fixed position until the .force produced by thebimetallic member again equals, or is greater than, the two-ouncesetting of the resilient member 28. When the bimetallic member 28 doesdevelop a force equal to or greater than two ounces, the free endthereof, in cooperation with the impact pin 24,

' will return to its original fixed or first static position with a snapaction, in a manner herelnabove described.

It is, therefore, obvious that due to the predetermined conflguration ofthe resilient member 28 and the mounting of impact pin 24 uponsubstantially the central portion of the resilient member 28, suchresilient member 26 insures a snap action of the bimetallic member 28and the impact pin 24, and therefore. prohibits any creeping action ofthe bimetallic member When assembling the thermostat ill, the notch 88oi contact arm 28 is positionedwithin the slot 12 of impact pin 24. Thenotch I2 has a width of substantially 2A as shown on Figs. 2 and 21 plusthe thickness of the contact arm 28. This permits the impact pinassembly to move a distance of 2A from a static position before thecontact arm 28 is engaged.

The contact arm 28 has a distance of travel between the upper and lowercontacts l6 and i8 of 23 shown on Figs. 2 and 21. Accordingly. theimpact pin assembly moves a distance of 2A plus 213 before it isrestrained in its travel by ill the engagement of the movable contactswith the second set of stationary contacts I8 or l8. It will beunderstood that, when the impact pin assembly 25 has traveled a distanceof 2A plus B, the contact arm 20 will be substantially in itsneutral.position. It, therefore, follows that during the last 13distance of travel the resilient member 22, located upon the contact arm20, will aid such travel and ensure a snap-action of the contacts withan increased making contact pressure. This contact pressure, at theconclusion of a making operation, is shown as C' on Fig. 21, in contrastto total contact pressure of E.

It is, therefore, obvious that inasmuch as the impact pin assembly movesa distance of 2A before engaging the contact arm 20, the contacts willbe prevented from creeping. Accordingly, it

is apparent that the thermostat would be snapacting in operationregardless of the type or character of the heat-responsive device.

With the thermostat It operatively associated with a plurality ofcircuits (not shown) and the bimetallic member 28 operatively associatedwith a body such as a water heater (not shown) that is heated inaccordance with the operation of such thermostat, the thermostat will,due to the operation of the bimetallic member 28, control the operationsof the circuits, as hereinafter described. The number of controllablecircuits depends upon the number of contacts mounted upon contact arm 28and insulated support it, as will be understood. Since such circuits arewell known in the art and form no part of my present invention, I havenot deemed it necessary to illustrate the same.

Assmning that the movable contact arm' 20, the impact pin 24 andbimetallic member 28 are in their lower positions, and that thebimetallic member 28 is subjected to the body (not shown) which is beingheated, the bimetallic member 28 will attempt to bend or flex upwardlyas such body is heated. However, due to the downward biasing action ofthe main resilient member 26.

through impact pin 24 on the bimetallic member 28, such bimetallicmember will remain in its original position until the upward forceproduced therein exceeds the downward biasing action of the resilientmember 26. This will occur when the heated body has arrived at thepredetermined set value, at which it is desired to disconnect the powersupply from the heating element. When the upward force produced by thebimietallic member 28 slightly exceeds the downward biasing action oi.the spring 26, the impact pin 2! wilFbe moved upwardly with a snapaction, in a manner hereinabove described.

Due to the cooperative action of impact pin assembly 25 and movablecontact arm 20, the bimetallic member 28 and impact pin 24 will move adistance 2A, as hereinabove described and shown orrgraph (Fig. 21),before the impact pin 24 contacts the movable contact arm] 20. By thetime the impact pin 24 strikes the movable contact arm 20, such pin hasattained a suflicient momentum or kinetic energy in addition to theupward force of the bimetallic member 28- to cause the movable contactarm to be carried across the air gap 2B.

As the impact pin 24 first strikes contact arm 20, it need only movesuch contact arm a distance B before the action of its cooperatingresilient member 22 would cause such arm to proceed on with a snapaction, as hereinabove described. However, the impact pin 24 and contact arm 20 will move together, resulting in a contact pressureimmediately following the operation of the thermostat substantiallyequal to E, shown in Fig. 21. At the conclusion of this operation, thepower supply will be disconnected from the heating element and theheated body will slowly cool.

The bimetallic member 28 will then tend to reverse its flexure as thebody cools, producing a force in an opposite direction from thatresulting in its original operation. The large contact pressureimmediately following the operation will then be reduced, to that shownas C in Fig. 21,

which is the amount due to the resilient member 22 biasing the movablecontact arm 20 against the stationary contacts It or l8. It, therefore,

follows that the movable contact arm 29 will be biased against thestationary contacts, with a minimum positive force 0 or C, regardless ofthe position of the contacts or the heating cycle, except during theswitching operation.

As the body continues to cool, the bimetallic member will bias theimpact pin towards the original position with an increasing force. Thenas the bimetallic member again overcomes the reverse action of theresilient member 25, the thermostat will operate in its reverse cycle ina manner similar to that hereinabove described. However, in this casethe bimetallic member 28 will force the impact pin downwardly againstthe action of the resilient member 25.

The impact pin assembly again moves a distance of 2A before engagingcontact arm 22. The contact arm 20 also moves a distance of 218 with theimpact pin assembly 25 before the movable contacts ii and lowerstationary contacts i8 reengage. This action will also be snap-acting ina manner hereinabove described.

It is, therefore, obvious that a thermostat built in accordance with myinvention will he snapacting in action in both directions, regardless ofthe number of contacts embodied therein, and that such thermostat willbe made so snap-acting, due, among other things, to the action of thesecond resilient member which, while being rigidiy attached to theheat-responsive device, nevertheless decreasingly resists the movementof the heat-responsive device from an initial static position.

It is further obvious that due to the ability to regulate the operationof the heat-responsive device, by means of adjusting the vertical actionof resilient member 26, the thermostat may be adjusted to operate onpractically any desired tem-' perature amplitude; and that, due to theruggedness of the assembled thermostat, such thermostat will not becomeunadjusted regardless of the amount of shock or vibrations to which itmay normally be subjected.

Various modifications may be made in the device embodying my inventionwithout departing i'rom the spirit and scope thereof, and I desire,therefore, that only such limitations shall be placed thereon as areimposed by the prior art and the appended claims.

I claim as my invention:

1. A heavy-duty thermostat, including a stationary and a cooperatingmovable contact, a heat-responsive device for operating said movablecontact, a first resilient member for movably supporting said movablecontact, and means comprising a second resilient member compressed intoan elastic curve for producing asnap action oi said device and movablecontact.

movable contact, a resilient member for movably supporting said movablecontact, said resilient member being rigidly attached to the movablecontact, a heat-responsive device, a frictionlessly operated resilientmember for biasing the heatresponsive device for snap action, and meanscomprising the heat-responsive device and the first-named resilientmember for producing a snap action of the movable contact.

4 In a thermostat including a casing, a frictionless resilient memberrigidly attached to the casing and compressed into an elastic curve, a

bimetallic heat-responsive device biased for snap action by saidresilient member, a contact bar movably mounted within the casing, asecond resilient member confined to an elastic curve and rigidlyattached at both ends to the contact bar for biasing thecontact bar forsnap action, and means including the snap action of the bimetallicheat-responsive device for producing snap action of the contact bar.

5. In a thermostat comprising, in combination, a casing, a frictionlessresilient member rigidly attached to thecasing and compressed into anelastic curve, an impact pin rigidly attached to substantially thecentral portion of the resilient member, a bimetallic heat-responsivedevice rigidly attached at one end thereof to the casing and operativelyassociated with the impact pin at the other end thereof for producing asnap action of the heat-responsive device, a shoulder pin attached tothe casing, a contact bar loosely mounted to the casing at one end bymeans of a shoulder pin, and a second resilient member confined to anelastic curve and rigidly attached at its end to the contact bar formovably supporting the second end of the contact bar and for producing asnap action of such contact bar.

6. A thermostat including a plurality of cooperating contacts, a movablecontact arm for supporting one of the contacts, and a resilient membermovably supporting the contact arm, said resilient member being rigidlyattached at both ends thereof to the arm with substantially amass?one-half thereof on one side of the arm and the other half on the otherside of the arm.

'7. A thermostat including a plurality of cooperating contacts, amovable contact arm for supporting one of the contacts, and a resilientmember movably and adjustably supporting the contact arm, said resilientmember being rigidly attached at both ends thereof to the arm andextending through the arm with substantially onehalf thereof on one sideof the arm and the other 10 half on the other side of the arm.

8. A thermostat including, in combination, a supporting structure, aplurality of cooperating contacts, a movable contact arm for supportingone of the contacts, a resilient member movably 5 supporting the contactarm, and an adjusting pin operatively associated with the supportingstructure and resilient member for adjusting the operation of thecontact arm, said resilient member being rigidly attached at both endsthereof to the 10 contact arm and extending through the arm withsubstantially one-half thereof on one side of the arm and the other halfon the other side of the arm, the adjusting pin being attached tosubstantially the central portion of the resilient member,

9. A thermostat including, in combination, a movable contact arm, aresilient member biased into an elastic curve and rigidly attached tothe contact arm, and a second resilient member operatively associatedwith the first resilient member for producing a snap-acting motion ofthe contact arm.

10. A thermostat including, in combination, a casing, a movable contactarm, a resilient member biased into an elastic curve and rigidlyattached to the contact arm, and a second resilient member operativelyassociated with the first resilient member and rigidly attached to thecasing for producing a snap-acting motion of the contact arm, and meansattached to the second resilient member and operatively associated withfirst resilient member and contact arm for retaining the secondresilient member within a double elastic curve.

' 11. A thermostat comprising, in combination, a plurality ofcooperating contacts including a movable contact, an impact pinoperatively associated therewith, a plurality of resilient mem-- bers,one of which is adapted to actuate said movable contact, and aheat-responsive device, the other of said resilient members and saidheatresponsive device being fitted to the impact pin and said oneresilient member loosely contacting said pin to produce snap-actingmovement of the movable contact at a predetermined temperature 5 settingof the heat-responsive device.

EARL K. CLARK.

